This invention relates to an intake system of an internal combustion engine, and more particularly to an improvement on an induction passage for achieving agitation and a thorough homogenization of an air-fuel mixture in an intake port.
For internal combustion engines, it has been considered and in some cases put into practice to promote homogenization of an air-fuel mixture admitted into the engine by producing a turbulent flow of the mixture upon its entrance into the combustion chambers thereby to attain an improved combustion characteristic through an increased burning rate. This is particularly effective for maintaining a stable engine operation under low load conditions including idling.
Methods proposed hitherto to accomplish this object include, for example, constricting an induction passage in a portion near the combustion chambers to accelerate an air-fuel mixture flow, lessening the lift of intake valves instead of constricting the induction passage, and providing a particularly shaped shroud to each intake valve so as to forcibly vary the direction of the flow of the admitted air-fuel mixture, for example, to a direction circumferentially of the combustion chamber.
A disadvantage common to these prior art methods is that the employment of a flow-stimulating means as mentioned above becomes a significantly great intake resistance during full-throttle operation of the engine and hence causes lowering of the charging efficiency and maximum power of the engine.